Molecular mechanisms of signal reception and transduction in taste and smell are being studied. Particular emphasis is placed on studies of G-protein mediated signaling. Little is known about the molecular mechanisms involved in taste sensation. However, there are indications that both sweet and bitter taste detection involve G-protein mediated processes. Taste-tissue cDNA libraries are being analyzed to characterize gene expression in the circumvallate papilla. The molecular components of olfactory signal transduction in the main olfactory epithelium and vomeronasal organ are also being studied to help elucidate mechanisms involved in odor sensation. Three very large gene families of putative chemosensory receptors are expressed at high levels in small sub-populations of olfactory or vomeronasal neurons. The expression patterns and properties of all three families of putative odorant and pheromone receptors suggest that small groups of receptor cell with distinct ligand binding properties exist and are responsible for odor discrimination. These receptors are not only likely to be the primary means whereby chemicals are distinguished but also provide molecular markers for dissection of mechanisms involved in generation and maintenance of the organization of the main and accessory olfactory systems.